The objective of this project is to identify quantitatively field mechanisms of interaction in blood due to either fluid flow (rate-of- shear) or externally applied fields (electric or magnetic). Two such effects that have been documented recently are the delay of in vitro thrombus formation due to either increasing rate-of-shear in the flow or the application of an external magnetic field. The efforts of this research will be focused on the working hypothesis that the mechanism which results in these effects is the preferential alignment of one or more of the macromolecular participants in the in vitro thrombus- formation process. Fresh whole blood (wb) or platelet-rich-plasma (prp) from fasted normal donors will be used to produce coagula under the controlled in vitro flow conditions of a modified Chandler rotating loop system. The effects to be studied include: a) the dependence of thrombus-formation time in prp and wb on field strength and rate-of-shear, b) the dependence of thrombus structure in wb and prp on field strength and rate-of-shear. The reduced sedimentation of erythrocytes in whole blood or single protein solutions in a transverse field will be examined theoretically and experimentally in order to identify orientation effects. Solutions of single blood proteins will be examined using the optical techniques of spectrophotometry, spectropolarimetry and birefringence to quantify their orientation in a transverse magnetic field.